1. Field of the Invention
The present invention relates to a fuel tank cap for use on a filler neck of an automotive fuel tank, and more particularly to such fuel tank cap having enhanced air-tight and liquid-tight characteristics.
2. Prior Art
Gaskets and sealing members for conventional fuel tank caps for automobiles are usually made of synthetic rubbers such as nitrile-butadiene rubber (hereinafter referred to NBR) that has been widely used for its inexpensiveness. However, such NBR gaskets are much more likely to swell and to suffer from resultant defects when submerged in hydrocarbons such as gasoline than would be if gaskets were made of fluorinated rubber or fluorosilicone rubber which is relatively costly. Accordingly, when the gasoline comes into contact with the NBR gasket of the cap mounted on the fuel filler neck, the gasket swells and its peripheral portion becomes hung down or dangled. Such dangled peripheral portion tends to be folded over on itself during re-installation of the cap on the filler neck, with the result that fuel leakage can occur through the cap. Further, the swollen gasket is prone to become shifted from a support bracket and thus to be held against the filler neck out of the proper position, allowing the fuel to be spilled. Sealing rubber members when swollen are liable to be placed out of a retainer and the bracket, thereby causing fuel leakage.